Road vulnerability and the dynamics of rainfall along Igbara-Oke road, Ondo State, Southwestern Nigeria

Abstract

This research showed the significance of rainfall, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity method for road vulnerability along Igbara Oke road, Ondo State, Nigeria. In doing this, a geophysical approach has been adopted with the use of two geophysical methods involving Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity method using Lateral Resistivity Profiling (LRP) and Vertical Electrical Sounding techniques (VES) for a distance of more than half a kilometer. The lateral resistivity profiling allowed for evaluation of lateral variation in resistivity with respect to a fixed depth while the vertical electrical sounding for the understanding of the layer stratification of the study area in term of thickness and layer resistivity. VLF-EM was engaged to define the study area with respect to conductive and resistivity zone, while the methodological data of rainfall pattern within the last ten years was engaged to understand the dynamics of rainfall within this period. The Wenner profiling has a resistivity distribution/variation ranging between 16 to 520 Ωm, while VLF -EM profiling was characterized by conductivity ranging from 0.1 to 2.0 % and -0.1 to -4.1%. Vertical electrical sounding identified three to four geoelectric sections which are topsoil, weathered layer, fractured basement and fresh basement with varying resistivity and thickness. The results from the VES was used to determine the second order parameters for better understanding of the dynamic nature of the subsurface that may lead to further vulnerability. The rainfall data exhibits the reasons for the unprecedented vulnerability witnessed in recent years, coupled with the geological factors, and hence, the possible solution towards securing a sustainable future in foundations especially on road construction.